An induction motor comprises a stator which generates a revolving magnetic field inside a cavity and a rotor which is rotatably arranged inside the cavity of the stator and rotates by interaction with the magnetic field generated by the stator.
The stator comprises a stator stack defining the cavity and a stator winding which is wound on the inner peripheral portion of the stator stack. When a current flows through the stator winding, a magnetic field is generated inside the cavity.
The rotor comprises a rotor stack and a rotor cage with a rotary shaft. The rotor cage is formed by a pair of end rings and a plurality of conductive bars formed between the pair of end rings.
When the rotor is rotatably disposed inside the cavity of the stator and a current flows through the stator winding, the magnetic field generated by the stator winding is applied to the rotor. This in turns generates a current in the conductive bars and an electromagnetic force is generated in the rotor due to the interaction between the current generated in the conductive bars and the magnetic field generated by the stator. The rotor rotates due to the electromagnetic force generated in the rotor.
In the magnetic and the electric circuits of the motor (stator and rotor stacks, stator winding and rotor cage) power losses are present due to the electromagnetic power conversion. These losses generate heat which has to be removed to maintain the temperature of the components compatible with the materials thermal class properties and the desired level of reliability of the motor.
In order to remove the generated heat, the motor is provided with an air circulation cooling system.
In the state of the art, it is known to provide fins on the outer surface of the housing of the motor and a fan assembly on the non-drive side of the motor to generate and direct an airflow toward the fins.
For example, induction motors with cooling systems are disclosed in US 2014/0062227, US 2014/0021812 and US 2011/0068644.
Since a relevant amount of losses is caused by the heat generated in the rotor, the Applicant has perceived that the cooling fins are just about sufficient to remove the heat generated in the rotor, and that the motor performance can be increased by improving the rotor cooling.
Therefore, a need arises to provide an induction motor with a cooling system involving improved cooling of the rotor.